﻿/**
* Stemmer, implementing the Porter Stemming Algorithm
*
* The Stemmer class transforms a word into its root form.  The input
* word can be provided a character at time (by calling add()), or at once
* by calling one of the various stem(something) methods.
*/

class Stemmer {
    private char[] b;
    private int i,     /* offset into b */
            i_end, /* offset to end of stemmed word */
            j, k;
    private const int INC = 50;
    /* unit of size whereby b is increased */
    public Stemmer()
    {
        b = new char[INC];
        i = 0;
        i_end = 0;
    }

    /**
     * Add a character to the word being stemmed.  When you are finished
     * adding characters, you can call stem(void) to stem the word.
     */

    public void add(char ch)
    {
        if (i == b.Length)
        {
            char[] new_b = new char[i + INC];
            for (int c = 0; c < i; c++) new_b[c] = b[c];
            b = new_b;
        }
        b[i++] = ch;
    }


    /** Adds wLen characters to the word being stemmed contained in a portion
     * of a char[] array. This is like repeated calls of add(char ch), but
     * faster.
     */

    public void add(char[] w, int wLen)
    {
        if (i + wLen >= b.Length)
        {
            char[] new_b = new char[i + wLen + INC];
            for (int c = 0; c < i; c++) new_b[c] = b[c];
            b = new_b;
        }
        for (int c = 0; c < wLen; c++) b[i++] = w[c];
    }

    /**
     * After a word has been stemmed, it can be retrieved by toString(),
     * or a reference to the internal buffer can be retrieved by getResultBuffer
     * and getResultLength (which is generally more efficient.)
     */
    public string toString() { return new string(b, 0, i_end); }

    /**
     * Returns the length of the word resulting from the stemming process.
     */
    public int getResultLength() { return i_end; }

    /**
     * Returns a reference to a character buffer containing the results of
     * the stemming process.  You also need to consult getResultLength()
     * to determine the length of the result.
     */
    public char[] getResultBuffer() { return b; }

    /* cons(i) is true <=> b[i] is a consonant. */

    private bool cons(int i)
    {
        switch (b[i])
        {
            case 'a':
            case 'e':
            case 'i':
            case 'o':
            case 'u': return false;
            case 'y': return (i == 0) ? true : !cons(i - 1);
            default: return true;
        }
    }

    /* m() measures the number of consonant sequences between 0 and j. if c is
       a consonant sequence and v a vowel sequence, and <..> indicates arbitrary
       presence,

          <c><v>       gives 0
          <c>vc<v>     gives 1
          <c>vcvc<v>   gives 2
          <c>vcvcvc<v> gives 3
          ....
    */

    private int m()
    {
        int n = 0;
        int i = 0;
        while (true)
        {
            if (i > j) return n;
            if (!cons(i)) break; i++;
        }
        i++;
        while (true)
        {
            while (true)
            {
                if (i > j) return n;
                if (cons(i)) break;
                i++;
            }
            i++;
            n++;
            while (true)
            {
                if (i > j) return n;
                if (!cons(i)) break;
                i++;
            }
            i++;
        }
    }

    /* vowelinstem() is true <=> 0,...j contains a vowel */

    private bool vowelinstem()
    {
        int i; for (i = 0; i <= j; i++) if (!cons(i)) return true;
        return false;
    }

    /* doublec(j) is true <=> j,(j-1) contain a double consonant. */

    private bool doublec(int j)
    {
        if (j < 1) return false;
        if (b[j] != b[j - 1]) return false;
        return cons(j);
    }

    /* cvc(i) is true <=> i-2,i-1,i has the form consonant - vowel - consonant
       and also if the second c is not w,x or y. this is used when trying to
       restore an e at the end of a short word. e.g.

          cav(e), lov(e), hop(e), crim(e), but
          snow, box, tray.

    */

    private bool cvc(int i)
    {
        if (i < 2 || !cons(i) || cons(i - 1) || !cons(i - 2)) return false;
        {
            int ch = b[i];
            if (ch == 'w' || ch == 'x' || ch == 'y') return false;
        }
        return true;
    }

    private bool ends(string s)
    {
        int l = s.Length;
        int o = k - l + 1;
        if (o < 0) return false;
        for (int i = 0; i < l; i++) if (b[o + i] != s[i]) return false;
        j = k - l;
        return true;
    }

    /* setto(s) sets (j+1),...k to the characters in the string s, readjusting
       k. */

    private void setto(string s)
    {
        int l = s.Length;
        int o = j + 1;
        for (int i = 0; i < l; i++) b[o + i] = s[i];
        k = j + l;
    }

    /* r(s) is used further down. */

    private void r(string s) { if (m() > 0) setto(s); }

    /* step1() gets rid of plurals and -ed or -ing. e.g.

           caresses  ->  caress
           ponies    ->  poni
           ties      ->  ti
           caress    ->  caress
           cats      ->  cat

           feed      ->  feed
           agreed    ->  agree
           disabled  ->  disable

           matting   ->  mat
           mating    ->  mate
           meeting   ->  meet
           milling   ->  mill
           messing   ->  mess

           meetings  ->  meet

    */

    private void step1()
    {
        if (b[k] == 's')
        {
            if (ends("sses")) k -= 2;
            else
                if (ends("ies")) setto("i");
            else
                    if (b[k - 1] != 's') k--;
        }
        if (ends("eed")) { if (m() > 0) k--; }
        else
            if ((ends("ed") || ends("ing")) && vowelinstem())
        {
            k = j;
            if (ends("at")) setto("ate");
            else
                if (ends("bl")) setto("ble");
            else
                    if (ends("iz")) setto("ize");
            else
                        if (doublec(k))
            {
                k--;
                {
                    int ch = b[k];
                    if (ch == 'l' || ch == 's' || ch == 'z') k++;
                }
            }
            else if (m() == 1 && cvc(k)) setto("e");
        }
    }

    /* step2() turns terminal y to i when there is another vowel in the stem. */

    private void step2() { if (ends("y") && vowelinstem()) b[k] = 'i'; }

    /* step3() maps double suffices to single ones. so -ization ( = -ize plus
       -ation) maps to -ize etc. note that the string before the suffix must give
       m() > 0. */

    private void step3()
    {
        if (k == 0) return; /* For Bug 1 */ switch (b[k - 1])
        {
            case 'a':
                if (ends("ational")) { r("ate"); break; }
                if (ends("tional")) { r("tion"); break; }
                break;
            case 'c':
                if (ends("enci")) { r("ence"); break; }
                if (ends("anci")) { r("ance"); break; }
                break;
            case 'e':
                if (ends("izer")) { r("ize"); break; }
                break;
            case 'l':
                if (ends("bli")) { r("ble"); break; }
                if (ends("alli")) { r("al"); break; }
                if (ends("entli")) { r("ent"); break; }
                if (ends("eli")) { r("e"); break; }
                if (ends("ousli")) { r("ous"); break; }
                break;
            case 'o':
                if (ends("ization")) { r("ize"); break; }
                if (ends("ation")) { r("ate"); break; }
                if (ends("ator")) { r("ate"); break; }
                break;
            case 's':
                if (ends("alism")) { r("al"); break; }
                if (ends("iveness")) { r("ive"); break; }
                if (ends("fulness")) { r("ful"); break; }
                if (ends("ousness")) { r("ous"); break; }
                break;
            case 't':
                if (ends("aliti")) { r("al"); break; }
                if (ends("iviti")) { r("ive"); break; }
                if (ends("biliti")) { r("ble"); break; }
                break;
            case 'g':
                if (ends("logi")) { r("log"); break; }
                break;
        }
    }

    /* step4() deals with -ic-, -full, -ness etc. similar strategy to step3. */

    private void step4()
    {
        switch (b[k])
        {
            case 'e':
                if (ends("icate")) { r("ic"); break; }
                if (ends("ative")) { r(""); break; }
                if (ends("alize")) { r("al"); break; }
                break;
            case 'i':
                if (ends("iciti")) { r("ic"); break; }
                break;
            case 'l':
                if (ends("ical")) { r("ic"); break; }
                if (ends("ful")) { r(""); break; }
                break;
            case 's':
                if (ends("ness")) { r(""); break; }
                break;
        }
    }

    /* step5() takes off -ant, -ence etc., in context <c>vcvc<v>. */

    private void step5()
    {
        if (k == 0) return; /* for Bug 1 */ switch (b[k - 1])
        {
            case 'a': if (ends("al")) break; return;
            case 'c':
                if (ends("ance")) break;
                if (ends("ence")) break; return;
            case 'e': if (ends("er")) break; return;
            case 'i': if (ends("ic")) break; return;
            case 'l':
                if (ends("able")) break;
                if (ends("ible")) break; return;
            case 'n':
                if (ends("ant")) break;
                if (ends("ement")) break;
                if (ends("ment")) break;
                /* element etc. not stripped before the m */
                if (ends("ent")) break; return;
            case 'o':
                if (ends("ion") && j >= 0 && (b[j] == 's' || b[j] == 't')) break;
                /* j >= 0 fixes Bug 2 */
                if (ends("ou")) break; return;
            /* takes care of -ous */
            case 's': if (ends("ism")) break; return;
            case 't':
                if (ends("ate")) break;
                if (ends("iti")) break; return;
            case 'u': if (ends("ous")) break; return;
            case 'v': if (ends("ive")) break; return;
            case 'z': if (ends("ize")) break; return;
            default: return;
        }
        if (m() > 1) k = j;
    }

    /* step6() removes a-e if m() > 1. */

    private void step6()
    {
        j = k;
        if (b[k] == 'e')
        {
            int a = m();
            if (a > 1 || a == 1 && !cvc(k - 1)) k--;
        }
        if (b[k] == 'l' && doublec(k) && m() > 1) k--;
    }

    /** Stem the word placed into the Stemmer buffer through calls to add().
     * Returns true if the stemming process resulted in a word different
     * from the input.  You can retrieve the result with
     * getResultLength()/getResultBuffer() or toString().
     */
    public string stem(string word)
    {
        add(word.ToCharArray(), word.Length);

        k = i - 1;
        if (k > 1) { step1(); step2(); step3(); step4(); step5(); step6(); }
        i_end = k + 1; i = 0;
        return toString();
    }
}